Construction of the Gasoline Engine. 529 



ward to reach the opening E in Fig. 258, which is the 

 same as F in Fig. 256. When this valve is closed it is at 

 H and is always controlled by the stem C worked by the 

 revolutions of the fly-wheels. 



The supply valve B is represented closed and is held 

 down by the spring K, which can be regulated by the ten- 

 sion given through the jamb-nut L. This valve is lifted 

 by the suction produced by the up-stroke of the engine pis- 

 ton. The opening G is a water jacket around the valves 

 to keep them cool. 



663. Igniting the Charge. There are two methods of ig- 

 niting the charge at the proper time, in these engines : one 

 is by means of an electric spark which is produced at just 

 the right time by means of a devise worked by the engine ; 

 the other is by means of a hot tube which rises out of the 

 chamber A, of Fig. 256, into the curved chimney standing 

 just to the left of C B. This tube is kept at the proper 

 temperature by means of a Bunsen burner fed through the 

 cock shown above F and at L, Fig. 257. After the charge 

 has been drawn in and the piston is coming down in the 

 cylinder so as to compress the gas, this compression forces 

 a part of the explosive mixture up into this hot tube and 

 when this is done the gas ignites and an explosion follows. 

 If this tube becomes too hot the tendency will be for it to 

 explode the charge too soon and either lessen the power of 

 the engine or reverse its motion. If it is too cold the ex- 

 plosion will be too late. After the tube has been used for 

 some time a scale may form over it which prevents the in- 

 ner wall from taking the proper temperature and it is then 

 necessary to replace it with a new one. In replacing this 

 tube it is necessary to use one which is adapted specially 

 to the engine because if it is too large or too small, or too 

 long or too short, its capacity will affect the time of the 

 explosion and it will not be correct. 



664. Lubrication. Cleanliness of all working parts of 

 the engine and proper oiling arc matters of prime impor- 



